Why hCG Doubling Times Are Important in Early Pregnancy

When your prenatal health care provider talks about hCG, they're referring to human chorionic gonadotropin (aka "the pregnancy hormone"), which is produced by the placenta during pregnancy. The presence of hCG confirms a pregnancy, and measuring hCG levels can help health care providers gather information about the fetus.

The levels of hCG in a pregnant person’s blood rise rapidly in early pregnancy, doubling every two to three days on average. This is known as hCG doubling time.

When hCG levels don't rise as expected, it could be a cause for concern. But many pregnant people with lower-than-expected hCG levels or slower-than-average doubling times go on to have healthy pregnancies and babies.

Here's what you need to know about testing for hCG, including when hCG stops doubling and what hCG levels say about the health of the pregnancy.

Testing hCG Levels in Pregnancy

The two most common tests for hCG levels differ not only in how they are done but also what they can reveal.

• Qualitative test: This type of test only detects the presence of the hormone (starting around 12 to 14 days after conception). A urine test like the pee-on-a-stick pregnancy test available at drugstores is a qualitative test.
• Quantitative test: This determines the actual amount of the hormone in the body by testing a blood sample. A quantitative test (also known as a beta hCG test) can detect the hormone sooner, about 11 days after you conceive.

For a quantitative test, hCG is measured in milli-international units per milliliter (miU/ml). An hCG level above 5 mIU/ml is a positive indicator of pregnancy. Anything less than that is considered a negative pregnancy test.

While quantitative blood tests can be useful, not all health care providers routinely order them to confirm pregnancy. Many will use a transvaginal ultrasound to confirm the pregnancy instead.

Typical hCG Doubling Times

In a typical pregnancy, hCG levels double every 48 to 72 hours. This period increases to about every 96 hours as you get further along. HCG levels peak during the first eight to 11 weeks of pregnancy, then decline and plateau.

Healthy hCG levels can vary significantly from pregnancy to pregnancy, and there's a very wide range of what's considered normal. When health care providers monitor hCG levels, they're looking for the levels to fall within the expected range for gestational age and for the levels to double within the expected timeframe.

What hCG Doubling Times Can Show

Until about six or seven weeks after your last menstrual period, checking hCG doubling times is a good way to monitor whether a pregnancy is progressing normally.

After that, ultrasounds become the best tool for getting information on how the pregnancy is developing, and they're more accurate than hCG numbers. Transvaginal ultrasounds are most common in the first trimester, while abdominal ultrasounds are conducted in later trimesters.

When Does hCG Stop Doubling?

You can usually expect your hCG level to stop rising between week eight and week 11 of pregnancy. That is the time during which the hormone tends to reach its peak.

Keep in mind, however, that every pregnancy is different, so these are just ballpark estimates for when hCG stops doubling.

Causes of Slow-Rising hCG Levels

Slow-rising hCG doubling times can be a sign of miscarriage or a symptom of ectopic pregnancy (when the fertilized egg implants outside of the uterus, such as in the fallopian tubes, and can't survive). But this is not always the case.

The two- to three-day doubling guideline holds true in 85% of normal pregnancies. That means that about 15% of viable pregnancies may have slower hCG doubling times, so it's not always a cause for concern.

That said, any hCG level that decreases in the first trimester is almost always a sign of miscarriage.

Causes of Higher-Than-Usual hCG levels

High hCG levels also have meaning. For example, they might indicate:

• Miscalculated conception date (you're farther along in your pregnancy than originally thought)
• Molar pregnancy (a nonviable pregnancy that develops into a tumor)
• Multiple pregnancy (being pregnant with two or more babies)

Finding out that your hCG levels are atypical can be very stressful and upsetting, so it's important to remember that slower (or faster) hCG doubling times don't always indicate an issue with your pregnancy. Talk to your health care provider about any concerns.